1. Field of the Invention
The present invention relates to an angle measuring method and an angle measuring apparatus, which employ a projection type display.
2. Description of the Prior Art
In recent years, displays are developed for a larger screen, higher image quality and higher functions. As one example of a display having a large screen, a projection type display is well known in which an optical image is formed on a light valve and light is irradiated to the optical image such that the optical image is projected onto a screen on an enlarged scale by a projection lens.
However, in the known projection type display, a projector should be placed in front of the screen such that a normal vector of a face of the screen coincides with that of a liquid crystal panel. Otherwise, graphic distortion will be produced in an image on the screen. Thus, in order to place the projector at other locations than a front of the screen, it is necessary to perform calculation for correcting graphic distortion on the screen, which is produced when the projector is placed at other locations than the front of the screen. Furthermore, in order to perform calculation for correcting graphic distortion, positional relation between the screen and the projector is required to be grasped completely. To this end, angles of inclination of the screen and the projector should be measured actually, which is quite troublesome and is difficult in some cases. For example, in case the screen is placed at a location difficult of access or a dangerous spot, it is difficult to actually measure angle of inclination of the screen.
Meanwhile, supposing that a projection type display in which the projector can be placed at other locations than the front of the screen is put on the market, the user should measure angles of inclination of the screen and the projector. In this case, a known procedure in which a protractor or the like is used for measuring the angles of inclination of the screen and the projector is quite unfamiliar to the user and thus, the product becomes quite difficult to use. In addition, unless the user is skilled in the measurement, accurate measurement may not be performed.
Therefore, in the prior art projection type displays, since actual measurement of angles of inclination of the screen and the projector is troublesome, difficult and quite unfamiliar to the user, it has been difficult to place the projector at other locations than the front of the screen.